1. Field
Embodiments of the present invention relate to systems and methods for performing nondestructive inspection. More particularly, embodiments of the present invention relate to automated systems and methods of performing nondestructive inspection of objects using a robot to move an inspection probe relative to the object under inspection.
2. Related Art
It is often desirable or required by law to perform a complete inspection of manufactured parts prior to shipment or use. Aircraft composite parts, for example, often require 100% inspection after manufacture to discover any defects such as excessive porosity, delamination, defective bonding, voids, and embedded foreign objects.
Nondestructive inspection is a commonly used method of performing a complete test of manufactured parts. Ultrasonic inspection is one form of nondestructive inspection that involves the use of ultrasound waves to inspect the interior portions of parts. Ultrasonic testing and other forms of nondestructive inspection are desirable in that they can be performed relatively quickly and do not require disassembly of the inspected parts.
Ultrasonic inspection equipment typically utilizes an ultrasound transducer or array of transducers (either of which may be referred to as a “probe”) to generate ultrasonic waves. Ultrasonic waves are similar to sound waves but have a much higher frequency, typically well beyond the range of human hearing. During ultrasonic inspection, the ultrasound probe is positioned near the surface of the part being inspected and oriented such that ultrasound waves generated by the probe are directed toward and through the part. When an ultrasound wave encounters a discontinuity in the part, such as a void, delamination or foreign object, part of the energy in the ultrasound wave is reflected. The reflected energy travels back through the part as a second ultrasound wave and is detected by the ultrasound probe, which acts as both a transmitter and receiver in what is commonly referred to as a “pulse echo” ultrasonic test system. The reflected ultrasound waves are collected and used to create a reflection signature, which may be expressed to the user in the form of an image or graph.
Ultrasonic inspection of large objects requires a person to manually move an ultrasound probe along the object under inspection as the inspection system emits ultrasound waves and collects inspection data. Such manual operation of the inspection system requires a person to monitor a sensor display to identify any defects in the structure. Alternatively, mechanical resolvers or encoders may be used to track the location of the transducer during the inspection process. Such mechanical resolvers may include friction-drive wheels that engage the part and roll along the part and sense movement of the transducer by generating signals indicative of movement of the wheels. The resolver (or encoder) generates a signal that the inspection system uses to associate the inspection data received from the probe with a location of the object under inspection. Using a resolver or encoder, the inspection system may generate and store an electronic image of the inspected part, obviating the need for a user to constantly monitor a sensor display during the inspection process.
It is sometimes desirable to further automate the process by using a robot to move the inspection probe relative to the part under inspection. When a robot is used in this manner the same challenges are present, namely, the position of the probe must be tracked with a resolver or encoder or a user must watch a display to identify any defects in the structure under inspection. While most robots are operable to periodically communicate position information, robots do not generate position information frequently enough for use with the inspection system. While a resolver or encoder addresses that problem by generating position information at a frequency that is compatible with the inspection system, the use of a resolver or encoder with a robot introduces additional challenges. The robot would need to be specially programmed or configured, for example, to keep the wheels in contact with the part under inspection. This introduces the possibility of errors and limits the speed at which the robot may be operated, thus mitigating some of the advantages of automation.